Well, there's one answer that says #2 and another that says #1. I personally believe the answer is #3, since its post-boil volume that sets the OG. It seems like there's no agreed-upon definition of this term, so I'm going to close this question.

When I'm brewing I typically think about what volume is going into the fermenters more than anything further down the line. This usually directly relates to what goes into the keg or into bottles but depends greatly on losses later in the process.

To twist dana's excellent example (and to be clear I do not completely disagree with his definition) when you make up a batch of batter the final number of pancakes depends greatly on the size of said pancakes (ok this is akin to bottle sizes so you're still good). However your ladle/scooping process will impact the number of pancakes since you will have losses to the bowel and to the scooper that aren't dependent on the batter recipe. So there's still a little room for interpretation.

I definitely agree that nothing pre-fermenter would in my mind be considered the batch size.

Haha! Who knew pancakes were so helpful. That's a good point, everyone's process is different so a batch might not equate to the same amount of packaged beer. It just seems cleaner to me to think of the finished product. I hate losing a bunch of beer to dry hops and trub and not filling a complete keg.
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danaDec 21 '11 at 18:53

Agreed! I hate the losses and try to minimize them but usually try to just up the batch size a bit to make up for some of it.
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Kevin ColbyDec 21 '11 at 18:56